In 1453, on this date, according to the Julian Calendar, the Tenth Crusade, led by united Christian forces directly under Pope Nicholas V gathered from a wide alliance of Venetian, German, and Genoese troops, broke the Ottoman siege at Constantinople.

Constantinople Siege RaisedIt would serve as the crowning moment of Nicholas' impressive eight-year term as pope and herald a new age of military security in Christendom from outside threats. Dubbed the time of the "Third Rome", the triumph would mean the end of the Byzantine period and domination over the European Muslims.

Constantinople grew up from the humble Greek town of Byzantium when Emperor Constantine decided to shift his capital in 330 to escape Roman factions and intrigue as well as establishing quick connection to frontiers where barbarian threats could arise. The Byzantine Empire continued even after the fall of Rome to German invasion and grew wealthy by controlling the key point of trade between the West and East as well as the Bosporus, the only shipping route from the Mediterranean to the Black Sea. Despite centuries of decline since the golden age of Justinian where the Byzantines dominated an empire almost as large as Rome's had been, Constantinople continued to hang on as a crucial lynchpin of world trade and civilization.

Meanwhile, the world changed around stagnant Constantinople. The Orthodox Church broke with the western Rome due to differences such as the veneration of icons and, especially, attacks such as the sacking of the Church of Holy Wisdom in 1204 during the Fourth Crusade. The Byzantines lost control of Anatolia, which broke into various principalities, one of which was ruled by Osman I in 1299, who held a vision of an empire as a tree with roots spreading through three continents and leaves blotting out the sky. He defeated the Byzantines at Bapheus in 1302, which was the first display of the quick expansion of the Ottomans through Anatolia and then, under Mehmed I, into the Balkans (1413-1421). Though the growing Ottoman Empire was just a few miles from Constantinople, it would be more than a century before they could muster enough force to conquer the city, merely demand tribute. Upon taking the Ottoman throne in 1451 at age nineteen, Mehmed II immediately set upon building up his navy and preparing to take Constantinople. He finally arranged a force estimated at around 100,000 soldiers with some 320 ships and established a blockade and siege in April of 1453.

A new story by Jeff ProvineAppeals from Constantinople did not go unheard, however. Pope Nicholas V began to call for a crusade for the liberation of the Bosporus from the Ottomans. No king seemed willing to head the expedition, and so Nicholas volunteered himself, using unprecedented powers hinted at in the declarations of Papal supremacy in the Council of Constance in 1418. He still needed armies, which he could gather freely as the Western Schism finally ended with the resignation of Antipope Felix V in 1449. While he would gather great support from Spain, France, and the Italian States, his greatest ally came as Frederick III, King of Germany, whom he crowned emperor of the Holy Roman Empire in 1450, on the condition that he aid in the pope's new crusade.

Just as the citizens of Constantinople were beginning to give up hope while seeing visions mysterious fogs darkened the city, a total lunar eclipse passed, and St. Elmo's fire was seen above the Church of Holy Wisdom, the Papal forces arrived. Winning the battle at sea, the crusaders cut off the Ottoman forces, who were in the midst of a final assault on Constantinople. The defenders held part of the city, and the Ottomans attempted to use defenses they had seized against the papal army. Eventually the Ottomans would be overwhelmed, and young Mehmed II would be killed in the fighting, which would rage for months to come as the crusaders stormed the rest of the Ottoman territories.

Rather than set the Byzantines up again, the territories were divided among the conquerors. Venice and Genoa received their outlying islands and sections of Greece while Frederick's empire expanded over much of the Balkans. Pope Nicholas would die in 1455, but he began the healing of the rift between Rome and Eastern Orthodoxy, which would be completed in a series of councils loosening strict dogma on political grounds. Nicholas's interest in humanism and the arts would be embraced, widening the Renaissance and establishing a new era of hierarchical unity through the Church, accepting reforms proposed out of Germany through men such as Luther and Calvin.

However, Nicholas's humanism would be notably prejudice in the religious superiority of Christendom. His expansion of slavery against "Saracens, Pagans and other enemies of Christ wherever they may be found" in the 1452 papal bull was meant originally to encourage conquest by Portuguese in Africa, but the rest of Christendom would seize the opportunity. A new world superpower increasingly centralized through the Holy Roman Empire and Holy League would sweep through the Middle East and North Africa in further crusades, wantonly conquering and eliminating other cultures for centuries until Enlightenment ideals of separating church and state sparked mass revolt.